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Endurance Exercise Training and Male Sexual Libido

1Department of Exercise and Sport Science, University of North Carolina, Chapel Hill, NC; and 2Department of Nutrition, Gillings School of Global Public Health, University of North Carolina, Chapel Hill, NC

Abstract

Purpose

This article aimed to study the associations between aspects of endurance exercise training and sexual libido in healthy men using a cross-sectional online survey study design.

Methods

A developed online survey questionnaire was used. The questionnaire was based on preexisting validated questionnaires and was used to assess elements of physical characteristics, exercise training habits, and libido of participants (n = 1077). Three evidence-based categories were created for the primary outcome of total libido score and low, normal, and high-response category sets. The high and normal categories were combined to form a high/normal score group, and the low category formed a low score group. Odds ratio (OR) values were calculated to examine group categorization.

Results

Age, training intensity, and training duration of participants had significant (P < 0.02) univariate relationships, with libido scores, and were thus included in the multivariate model. In the multivariate model, training intensity (P < 0.0001) and duration (P < 0.002) components were the most significantly associated with libido group designation (high/normal vs low). Participants with the lowest (OR = 6.9, 95% confidence interval [CI] = 2.6–17.9) and mid-range training intensities (OR = 2.8, 95% CI = 1.4–5.3) had greater odds of high/normal libido state than those with the highest training intensity. Participants with the shorter (OR = 4.1, 95% CI = 1.6–10.0) and mid-range training durations (OR = 2.5, 95% CI = 1.3–4.8) at their current intensity also had greater odds of high/normal libido score than those with a greatest duration.

Conclusion

Exposure to higher levels of chronic intense and greater durations of endurance training on a regular basis is significantly associated with a decreased libido scores in men. Clinicians who treat male patients for sexual disorders and/or council couples on infertility issues should consider the degree of endurance exercise training a man is performing as a potential complicating factor.

The Centers for Disease Control and Prevention reports that 1.5 million women in the United States (6%) are infertile (National Survey of Family Growth), and the American Society for Reproductive Medicine affirms that infertility affects men and women equally (2,29). Moreover, in approximately 40% of infertile couples, the male partner is either the sole cause or a key contributing cause of infertility (2). One of the factors influencing fertility in males is a low sexual desire; that is, decreased libido (2). Clinically decreased libido can manifest as Male Hypoactive Sexual Desire Disorder (Diagnostic and Statistical Manual of Mental Disorders V), which affects approximately 16%–18% of the adult male population (8).

It is well known that women who are involved with high levels of intensive exercise training have an elevated risk for developing menstrual dysfunctions and potential infertility, especially if they display “athletic amenorrhea” as a result of hypothalamic–pituitary–gonadal axis disruption (31). Evidence indicates that exercising men develop a similar corollary hypothalamic–pituitary–gonadal axis condition referred to as the “exercise hypogonadal male condition” (EHMC) (16). In the male condition, a quasi-hypogonadotropic hypogonadism exists as testosterone and luteinizing hormone levels are both suppressed; moreover, abnormal sperm characteristics are sometimes manifested (3,14). Current evidence links the development of EHMC to the combining effects of the volume and intensity of endurance exercise training in these men (3,14,16).

Testosterone is associated with many androgenic–anabolic processes in the male, and although not universally accepted, it is thought to play a key role in male sexual libido (6). Being more physically active has been shown to be beneficial reproductively for men who are sedentary (or have a very low physical activity levels) as it results in improved testosterone levels and libido (11,32). Conversely, there are many reports in the popular literature and on the Internet suggesting that men who participate in large amounts of endurance exercise training (e.g., marathon running) can have suppressed testosterone and libido (3,5). An examination of available peer-reviewed research literature, however, reveals the issue of libido status in males engaged in endurance exercise has not been systematically or empirically studied. To this end, we studied the associations between aspects of endurance exercise training and the libido status in healthy men using a cross-sectional online survey study design.

METHODS

Development of the survey instrument

An online survey questionnaire was developed to assess elements of physical characteristics, exercise training habits, and sexual libido of male participants. The questions concerning exercise training habits were based on the International Physical Activity Questionnaire and the Baecke Questionnaire and followed the recommendations of the American Heart Association (1,4,12). The libido-related questions were based on items within the Androgen Deficiency in the Aging Male Questionnaire, the Sexual Desire Inventory 2, and the Aging Male Symptoms Scale (18,19,23,27). The International Physical Activity Questionnaire, the Baecke Questionnaire, the Androgen Deficiency in the Aging Male Questionnaire, the Sexual Desire Inventory 2, and the Aging Male Symptoms Scale are commonly used in research-clinical settings, and the validity of each has been assessed and reported elsewhere (Cronbach's alpha = 0.70 to 0.96 (10,18–20,24,27)). The completed online survey was reviewed by an exercise physiologist and a fertility specialist who were not involved with the study to insure legitimacy of selected question items (i.e., content validity). The completed questionnaire and procedures for distribution were reviewed and approved by the University of North Carolina Institutional Review Board. Participant consent was obtained via their online access to the questionnaire, in which they also indicated they were healthy and free of endocrine-related medical disorders and prescription medication usage.

Survey sample—administration

The completed survey questionnaire was formatted into the Qualtrics® (Quatrics, 2014) online survey platform and made accessible through a specific world-wide web link (https://jfe.qualtrics.com/form/SV_eWESbBdaONSuUPb). Subsequent to establishment of the web link, a series of e-mail notifications were sent to sports clubs, national sports organizations, university athletic departments, and sporting magazines publicizing the existence of the survey and the web link site for access (~300 club/organizations were contacted). These e-mails requested announcement of the survey and encouragement of participation by individuals associated with the group/organization. The target population was adult males (>18 yr old) involved with sporting activities (e.g., walking, running, bicycling, and swimming) on a recreational and competitive basis in North America. However, clubs and organizations associated with endurance-based activities (e.g., running, triathlons, bicycling) were predominately targeted because EHMC is more prevalent in men engaged in such activities (3,14,16). The survey administration period was January 2014 to January 2015. Approximately every 4 months, reminder e-mails were sent to previous contacts to encourage them to continue to promote and distribute information about the survey.

Dependent measures

The survey was constructed in three parts. The first section addressed elements of the participant's eligibility for involvement (e.g., gender and medical status) and physical characteristics/demographic information. The second part focused on exercise habits and history of regular frequency of exercise (d·wk−1), intensity of training effort (number of light, moderate, and hard sessions per week), duration of exercise (hours per session and total hours per week), primary and secondary types—forms of exercise engagement, endurance sports competition participation (type and number of events), years in training, stability of training (i.e., our intent was to examine “standard” training and not periods of injury, tapering, or overreaching), focus of training (recreation, health, and sporting competition), and physical activity requirements at work (level of activity, min·d−1). Approximate oxygen uptake (V˙O2) percentages for respective exercise intensities (low [≤35%], moderate [50%], high [≥70%]) were selected based on the recommendations of Bouchard et al. (7). The third part of the survey addressed questions on libido, targeting such issues as sexual activity, arousal, desire, attraction, fantasy, appetite, fulfillment, needs for intimacy, and infertility issues or confounders (i.e., concussions and children sired).

Parts 1 and 2 of the survey allowed participants to click on predetermined answer button options, which provided appropriate ranges for each particular question and parameter being assessed. Part 3 (libido) involved a three-category format structure to the answer options where participants clicked answer buttons of yes, maybe, and no. Some follow-up questions were presented based on the answers. Answers to part three were scaled and scored in a Likert-type scale, with “yes” = 3, “maybe” = 2, and “no” = 1. Answers were assigned plus or minus values toward final libido score depending on the nature of the specific question. All libido questions (15 in total) were scored and an aggregate total libido score computed (i.e., >score = >libido).

Statistical analysis

All statistical analyses were conducted using IBM® SPSS ® v19 (2010). Frequencies and missing data checks were conducted to confirm data integrity (i.e., relative to missing data). Specific variables of interest included age categories, elements of exercise training intensity, and exercise training duration (see previous section) at the current levels of training, but all response variables were included in initial analyses. In addition, several exercise training variables were computed in which elements of frequency, intensity, and duration relative to time (hour per week and years of training) were integrated into composite scores to estimate overall dose of exercise effects. Tertile categories were created for the variables of interest listed previously, and three evidence-based categories were created for the primary outcome of total libido score (30). The cut points representing the libido score categories were as follows: low ≤ 7, normal 8–14, and high ≥ 15. The high and normal categories were combined to form a single high/normal score group, and the low category formed the low score group. Combining high/normal score groups was used because the focus of the study was on the presence and occurrence of lower libido in relation to endurance exercise training.

Demographic, exercise training, and libido characteristics of the participants were summarized using means, SD, and percentages. Demographic and exercise training outcomes potentially related to our primary outcome of libido score were analyzed using univariate statistics (chi-square analyses and t-tests). Subsequently, multivariable logistic regression (entry method) was used to determine adjusted odds ratio (OR) and 95% confidence interval (CI) for libido score (i.e., placement in high/normal vs low score group) for the factors with significant univariate relationships to libido score categories. Alpha level for all analyses was set to 0.05 a priori.

RESULTS

A total of 1366 individuals responded to the survey. Only respondents meeting all study criteria (n = 1077; healthy male and 18 yr or older, complete surveys, etc.) were included in the analyses. The mean ± SD physical characteristics and demographic outcomes of the participants are reported in Table 1.

The physical and exercise training characteristics of the participants.

Age, exercise training intensity, and training duration components of participants had significant univariate relationships (P < 0.02; Table 2) with libido scores and were thus included in the multivariate model. In the multivariate model, training “total intensity” (P < 0.0001) and “chronic duration” (P < 0.002) were significantly associated with libido score group designation (high/normal vs low). Total intensity was a computed variable representative of number of training sessions at a low, moderate, and hard intensity times the hours of each per week (~oxygen uptake [V˙O2] percent for respective intensities were low [≤35%], moderate [50%], and high [≥70%]) (see Methods). Chronic duration was a computed value representative of hours per week training times the number of years training (at current level).

Age was also a factor within the multivariate model. The youngest participants (≤40 yr; OR = 1.9, 95% CI = 1.0–3.9) and those in the middle age category (41–55 yr; OR = 1.9, 95% CI = 0.9–41) were more likely to be in the high/normal libido score group than those participants in the oldest age-category (≥56 yr).

Cronbach's alpha values within the current survey ranged from 0.64 to 0.88. These were slightly lower than the values originally reported from the survey/questionnaires on which the current one was based (see Methods).

DISCUSSION

In this cross-sectional survey study, we found that an inverse relationship exists between endurance exercise training factors and male libido scores. Specifically, higher amounts of intensive training or training involving greater amounts of duration within the endurance program were associated with lower libido scores. When comparing the OR responses among libido score classifications, participants in the low score group were approximately 64.5% to 85.5% ([1 − [1 / OR]] × 100) more likely to fall in that category because they did greater amounts of higher-intensity exercise. Also, the low libido score group was 60.0% to 75.6% more likely to fall into that category because they were doing greater amounts of longer duration exercise training (28). Conversely, the effect of low- to moderate-intensity training and shorter to moderate duration exercise training seemed highly comparable in clearly influencing the libido scores of the participants in a positive fashion, which is in support of previously published work (32).

To our knowledge this is the first scientific, research-based study to examine the issue of male libido and endurance exercise training. Several surveys on sexual habits and exercise training have been conducted previously by sporting magazines (e.g., Runners World) and sporting goods manufacturers (e.g., Brooks Sports Inc., Seattle, WA). However, the constructs of the questions presented in those surveys were not based on clinical assessment instruments used in sexual behaviors and fertility research. Furthermore, the statistical approaches used with these surveys tended to be descriptive in nature and not analytical–inferential.

Several recent laboratory studies have examined issues of sexual satisfaction and libido with exercise, but the generalizability applicability (to the current study) of those findings is hampered by the small sample sizes used (n < 20) and a focus on female participants (17,22). The findings of these latter studies did suggest that an acute exercise session enhances sexual arousal desire via activation of the sympathetic nervous system (SNS); enhanced SNS activity is a common response to a single bout of exercise (9). It is unclear if these aforementioned studies used habitual exercisers (such as within the current study). This last point is an important consideration as it is well established that exercise training improves the sensitivity of tissue responses to the SNS via enhanced receptor actions, resulting in substantially lower overall sympathetic autonomic neural tone after chronic training (9,15).

Our focus was to establish whether an association between libido and endurance training characteristics exists. As noted, an inverse relationship between duration/intensity characteristics of endurance training and libido was identified. However, the reason why increasing duration and/or intensity of exercise training reduces a male's libido score cannot be ascertained from the data obtained in this study. This study was not designed to explore a potential mechanism. As mentioned earlier, the presence of EHMC is more prevalent in endurance-trained men, and the condition is associated with lowered basal testosterone, which can be linked to reduced libido. However, currently the only means of detecting the existence of EHMC is through the measurement of reproductive hormonal levels within the blood or saliva. The present study did not ascertain hormonal profiles of the respondents. Hence, we cannot state whether EHMC was a direct factor in our participants with lower libido scores. Likewise, select medication use (e.g., performance-enhancing drugs), existing psychological disorders (i.e., depression), and/or chronic low caloric intakes are well-established factors associated with suppression of testosterone and reduced libido (13,14,26). For participation, we asked our male participants if they were healthy and not under medical supervision; thus, we feel the likelihood of these factors confounding our outcomes is unlikely. However, we are relying on our participant's truthfulness adherence and must acknowledge these were potential confounders in our data.

Increased volumes of intensive exercise training may also result in greater levels of physical and mental fatigue in an individual, which could reduce an individual's desire and motivation toward sex. In the current survey, we did not ask participants to report on their overall level of general fatigue or lethargy. Typically with excessive physical fatigue, experienced exercising individuals reduce their training loads to allow recovery (25). Our participants reported they were in a stable period of consistent training for several months at the time of the survey. This last fact also suggests that they were not overreaching/overtraining, which is associated with the development of the overtraining syndrome, which is linked to sexual dysfunction (15). Nonetheless, the influential aspects of general exercise fatigue from chronic exercise training as a possible causative mediator of reduced libido scores seem a logical likelihood and needs to be pursued in future research.

It was expected the age of the participants would be associated with libido score categorization. We found the participants in the two younger age-groups had a greater likelihood of placement in the high/normal libido score group than the oldest age-group. Evidence indicates that male libido does decrease with aging (13), and one could argue this was a factor influencing membership in the low libido score group. However, Lindau and Gavrilova (21) reported that medically healthy men of this age-group (i.e., ≥56 yr) have active sexual desires and not until 70–85 yr of age may there be sizable declines; that is, being ~50%–80% less than that observed 20–40 yr earlier in life. Relative to this last point, the OR observed for the influence of exercise training intensity and duration was of a significantly larger magnitude than that of age alone.

We acknowledge our sample was one of convenience, with potential response bias, and hence is a limitation. We also asked our subjects to complete the questionnaire only once, but with multiple reminder notices sent to organizations, it is possible some duplication occurred. Another aspect of our study that limits the interpretation and generalizability of the findings is our reliance upon self-reports and recall from our respondents. As a result of these factors, our findings should be viewed as preliminary in nature and more work on this topic is needed.

To conclude, this systematic study using an online survey approach suggests men engaged in higher intensities and greater durations of endurance training on a chronic basis (i.e., years) are significantly associated with decreased libido scores. Although our findings are preliminary, the results suggest that clinicians who treat male patients with regard to Male Hypoactive Sexual Desire Disorder and/or council couples on infertility issues should take into account the degree of endurance exercise training a man is performing as a potential complicating factor.

The authors wish to acknowledge the support of all the different sports clubs and organizations that aided in the distribution of our questionnaire. There was no internal or external funding in support of this project. The authors acknowledge there are no conflicts of interests relative to this work. Also, the results are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation, and the present study do not constitute endorsement by the American College of Sports Medicine.

29. U.S. Department of Health and Human Services. Fertility of Men and Women Aged 15–44 Years in the United States: National Survey of Family Growth, Centers for Disease Control and Prevention 2006–2010. Atlanta (GA): U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics; 2012; pp 4–5.

30. U.S. Department of Health and Human Services. Principles of Epidemiology in Public Health Practice. 3rd ed. An Introduction to Applied Epidemiology and Biostatistics. Atlanta (GA): U.S. Department of Health and Human Services, Centers for Disease Control and Prevention (CDC) Office of Workforce and Career Development; 2012; pp. 2-4–2-11.